by Jim Michaels, USA TODAY

by Jim Michaels, USA TODAY

WASHINGTON - The surge of U.S. forces in Afghanistan secured large portions of the country but has left pockets of Taliban in parts of the east, raising concerns that those strongholds could undermine progress as U.S. forces continue to leave the country, analysts say.

How much of a threat the Taliban poses is central to the debate on how many U.S. troops to leave behind after 2014, when Afghan forces assume responsibility for security. Any remaining troops would be used primarily for counterterror missions and to support Afghan security forces.

President Obama met with Afghan President Hamid Karzai at the White House on Friday and said he has not settled on the size of the force or the pace of the drawdown through 2014. The White House has said no option is off the table, including removing all troops after 2014.

Some military strategists, however, say the United States risks losing gains of recent years if the number of remaining U.S. forces is too small to stiffen the spine of Afghanistan's fledgling army and police force in the face of a continued Taliban threat.

Eastern Afghanistan's deep valleys and towering mountains have long served as a refuge for insurgent groups, including the Taliban and Haqqani network. Securing Kabul, the nation's capital, depends on the ability to control the approaches to the city, which run through the east.

"We have a fundamental problem in the east," said Fred Kagan, an analyst at the American Enterprise Institute who has advised top commanders in Afghanistan and Iraq. "The plan was always to shift resources from the south to the east, but the president's timeline for the surge recovery really prevented that from happening to any significant degree."

Obama ordered a surge of more than 30,000 U.S. troops into Afghanistan in December 2009. The vanguard of that surge flooded into Helmand province and Kandahar, key Taliban strongholds in the south.

But the pullout of the reinforcements began before the coalition could shift to the east, the next phase of the campaign.

Today, there are 66,000 American troops in Afghanistan, down from a peak of nearly 100,000 in 2010.

U.S. military officials say the Taliban has been driven to the margins of the country, making it difficult for them to influence or intimidate the population.

"We know the Taliban will remain resilient and capable in some areas, but they have largely been pushed out of the population centers," said Army Col. Tom Collins, a military spokesman in Kabul, in an e-mail.

The Taliban has "adapted somewhat by moving their operations and IED (improvised explosive devices) terror campaign into the countryside where civilians overwhelmingly remain the victims," Collins said.

Even if the Afghan and coalition forces can secure the key population centers, the presence of Taliban strongholds in the countryside can still pose a threat to Afghanistan's government, said Ronald Neumann, a former U.S. ambassador to Afghanistan.

The Taliban can use the isolated redoubts to launch attacks to cut roads and slowly claw its way back into power. The Soviets controlled key cities during their occupation in the 1980s but were ultimately defeated by the mujahedin, or Muslim freedom fighters, who fought from remote rural bases.

"They've seen repeated wars in which those who control large areas of the countryside unmolested win the war," Neumann said of Afghans.

Driving insurgents from rural strongholds will pose a major challenge for Afghan security forces, which lack the mobility and firepower of U.S. forces.

Afghanistan's military doesn't have enough aircraft to move forces quickly and then provide them with the supplies necessary to sustain operations. Roads in many parts of Afghanistan are primitive, making air mobility essential.

"You're putting the Afghans in a very precarious position," said Jeffrey Dressler, an analyst at the Institute for the Study of War.